1. Field of the Invention
This disclosure relates to an image forming apparatus provided with a sensor configured to detect a state of an object to be detected on an image bearing member such as a photosensitive member, an intermediate transfer member, and a transfer material bearing member.
2. Description of the Related Art
In the related art, an image forming apparatus using an electrophotographic process, a reference image formed on an image bearing member is read by a sensor as a detection device, an amount of misalignment from a reference obtained from a read result is calculated, and an amount of color-registration and an image density are corrected and maintained to adequate values. In this case, an optical sensor is used as the sensor. Examples of the image bearing member includes a photosensitive member, an intermediate transfer member, and a transfer material bearing member.
For example, in the case of a tandem-type image forming apparatus in which an intermediate transfer system is employed, reference images for a correction of color-registration in respective colors are formed on the intermediate transfer member by image forming units of respective colors, and positions of the reference images in the respective colors are detected by the sensor, whereby the correction of the color-registration is performed. In the image forming apparatus as described above, reference images for a correction of density in respective colors are formed on the intermediate transfer member by the image forming units of the respective colors, the density of the reference images of the respective colors are detected by the sensor, whereby the correction of density in the respective colors is performed.
Here, as one of causes which deteriorate detection accuracy of the sensor as described above, flapping of the reference images, which are objects to be detected is exemplified. For example, the intermediate transfer member of an endless belt shape is flapped in a depth direction of the sensor, the result of detection of the reference image varies. In order to avoid such a problem, a roller may be arranged at a position opposing a sensor on an inner peripheral surface side of the intermediate transfer member to restrain the flapping of the intermediate transfer member. However, when images (output images or reference images) transferred to a surface of the intermediate transfer member pass through a position on the roller having a potential difference with respect thereto, toner may fly around from the surface of the intermediate transfer member. As a result, the toner may fly toward a detection surface of the sensor arranged in proximity to the intermediate transfer member, and the flown toner may be adhered to the detection surface of the sensor.
As described in Japanese Patent No. 4724288, an openable-and-closable shutter member (protecting member) may be provided between the sensor and the intermediate transfer member.